showdown.js extension: match multiword extension

I want to create custom markdown tags using showdown.js such that:

==highlighted text==

renders:

<mark>highlighted text</mark>

Using the twitter extension as a baseline, I've been trying:

  // #highlighted# syntax
  {
    type:    'lang',
    regex:   '\\B(\\\\)?==([\\S]+)\\b',
    replace: function (match, leadingSlash, highlighted) {
      // Check if we matched the leading \ and return nothing changed if so
      if (leadingSlash === '\\') {
        return match;
      } else {
        return '<mark>' + highlighted + '</mark>';
      }
    }
  },

But this only lets me highlight single words, e.g.

• ==Apple ==Pear
• Apple Pear

I'd like to use == similar to **.

I assume the problem is the regex but can't seem to nail it. Can someone advise?

If I understand question correctly you can use this simple regex:

regex: "==\\s*(.+?)\\s*==";

and use matched group #1.

RegEx Demo